1. Field of the Invention
The present invention relates to internal combustion engines, and more particularly, to a loop scavenge two-cycle internal combustion engine and cylinder that use partial wall partitions and cooling ports to cool the cylinder and piston while still maintaining cylinder strength.
2. Description of the Related Art
In conventional two-cycle internal combustion engines using loop scavenge designs, scavenging paths convey compressed air-fuel mixtures from the crank chamber along the wall of the cylinder and into to the top of the cylinder. Typically, these scavenging paths are constructed in one of two ways: with wall partitions or without wall partitions. Designs using wall partitions completely separate scavenging paths from cylinder chambers such that the air-fuel mixture flowing through the scavenging path never contacts the side of the piston. In designs without wall partitions, a scavenging path is a channel formed along the inner wall of the cylinder with a side open to the piston. In this configuration, as the air-fuel mixture flows in the channel it contacts the side of the piston until it is discharged into the top of the cylinder. U.S. Pat. No. 4,934,345 discloses a loop scavenge engine without wall partitions.
The partitioned and non-partitioned designs offer mutually exclusive advantages. Using wall partitions increases cylinder strength and provides a more efficient scavenging operation in comparison to the non-partitioned design. In contrast, omitting the partitioning wall significantly improves cooling efficiency by applying cool fresh gas (air-fuel mixture) directly to the outer peripheral wall surface of the piston. In addition, the absence of partition walls decreases the weight of the engine, a significant advantage for applications requiring the user to move and handle the engine, e.g., chain saws and hedge trimmers. Thus, each design trades off one advantage for another, i.e., strength versus weight and scavenging efficiency versus cooling efficiency.
Therefore, there remains a need for a two-cycle engine loop scavenge system that incorporates all of the advantages of the partitioned and non-partitioned designs. The system should provide a lightweight engine with a strong cylinder that provides efficient scavenging as well as cooling.